Bar stock loaders are used with automatic screw machines having one or more spindles. Bar stock, generally from 8-12 feet in length, is fed from a magazine or hopper into a bar stock loader having bar stock retention members spaced along the length of the bar stock. In most instances, bar stock is cylindrical and requires no alignment between a bar being fed from the bar stock feeder to the automatic screw machine spindle as one segment of bar stock is depleted and a fresh length of bar stock is supplied to the spindle.
With cylindrical bar stock, a single operator can tend several automatic screw machines operating on cylindrical bar stock. The bar stock loader automatically provides a new segment of cylindrical bar stock to the automatic screw machine without the need for direct operator control.
Shaped bar stock having a triangular, square, hex, or other cross-section offers important advantages over cylindrical bar stock in some applications. By using shaped bar stock, machining operations necessary to form flats, or flat surfaces, on a workpiece can be eliminated. By eliminating machining steps to form flats, labor requirements, cycle times and tooling costs can be reduced or additional processing steps may be added. Prior art bar stock loaders required manual alignment of the flats of shaped bar stock with the flats of the bar stock in the automatic screw machine collet. Manual alignment increases labor requirements and reduces machine productivity.
For example, U.S. Pat. No. 3,664,215 discloses a machine tool having a spindle assembly operable to rotate non-circular bar stock about its longitudinal axis and a gripper assembly that engages a leading portion of the bar stock. The gripper is aligned with the chuck as the spindle is slowly rotated. This approach is slow and does not suggest synchronizing a fresh length of bar stock with a bar stock remnant at spindle operating speeds.
Similarly, U.S. Pat. No. 4,068,545 discloses an apparatus for feeding non-round cross-section bars to screw machines. A feed apparatus detects the rotational speed of the chuck and generates a speed output when the rotational speed lies in a low speed range. When the spindle rotates within a desired range, the controller actuates an electromagnet to withdraw an abutment, thereby allowing movement of the bar stock.
U.S. Pat. No. 5,456,146 discloses a bar stock pre-alignment collar prior to chucking in a collet. A plurality of spring-loaded veliers are used to urge flats of the bar stock into a pre-alignment position.
Thus, while the above patents have addressed, in part, the problem of aligning flats on bar stock, none of the patents provides an acceptable system for automatically synchronizing the rotation of a fresh section of bar stock with a bar stock remnant in the spindle or collet of an automatic screw machine. The prior art approaches impede machine productivity and require substantial operator intervention and supervision.
The solution to the above problems and other objects and advantages achieved by the invention are summarized below.